Method of processing tungsten halogen light bulbs

ABSTRACT

An improved method of processing tungsten halogen light bulbs is disclosed herein wherein the bulb envelope is filled with a forming gas and heated sufficiently to cause outgassing of oxides and/or other contaminants adsorbed or absorbed on the bulb wall and thereafter flashing the bulb filament while maintaining bulb wall heating such that the oxides and contaminants removed from the filament during flashing do not migrate to the bulb wall because the latter is sufficiently hot to prevent adsorption or absorption thereof, the contaminants from the filament and bulb wall being removed from the bulb envelope by subsequent application of a vacuum thereto.

United States Patent [1 1 Dolenga et al.

[ Aug. 26, 1975 METHOD OF PROCESSING TUNGSTEN HALOGEN LIGHT BULBS [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 27, 1973 [21] App]. No: 391,883

3,788,725 l/l974 Yannopoulos et a1 316/20 Primary ExaminerRoy Lake A.'Sistant Examtner-James W. Davie Attorney, Agent, or Firm-Peter D. Sachtjen 57 ABSTRACT An improved method of processing tungsten halogen light bulbs is disclosed herein wherein the bulb envelope is filled with a forming gas and heated sufficiently to cause outgassing of oxides and/or other contami nants adsorbed or absorbed on the bulb wall and thereafter flashing the bulb filament while maintaining bulb wall heating such that the oxides and contaminants removed from the filament during flashing do not migrate to the bulb wall because the latter is sufficiently hot to prevent adsorption or absorption thereof, the contaminants from the filament and bulb wall being removed from the bulb envelope by subsequent application of a vacuum thereto.

3 Claims, 2 Drawing Figures PATENTEU AUB25|975 3,901,573

FORMING FLUSHING id GAS 6A5 METHOD OF PROCESSING TUNGSTEN HALOGEN LIGHT BULBS The present invention relates to tungsten halogen light bulbs and, in particular, to an improved method of processing tungsten halogen light bulbs wherein contaminants are removed by simultaneously heating the bulb wall and flashing the filament to outgas adsorbed or absorbed contaminants.

The life of tungsten halogen light bulbs is adversely affected by various contaminants on the inner bulb wall or the filament. For instance, oxides on the filament or in the envelope material combine with the tungsten and/or halogen to interfere with the regenerative cycle or combine with hydrogen to form water which leads to water cycle erosion. Both of the above cause a reduction in bulb life.

To eliminate as many of these contaminants as possible, it has been common to use flashing of the bulb filament in the presence of a forming gas. The forming gas comprises a mixture of hydrogen and nitrogen which reduces the oxides normally on the surface of the tungsten filament and forms water in the vapor phase. This is subsequently removed by evacuation of the envelope. However, we have found that this processing is not completely satisfactory inasmuch as some of the oxides and/or other contaminants are redeposited on the cool bulb wall and are not removed by the aforementioned envelope evacuation.

Another processing technique employs vacuum outgasing to remove envelope contaminants. This involves heating the bulb wall of an evacuated bulb to a temperature at which contaminants on a wall are driven off the wall and out of the bulb. We have also found that this technique is not entirely satisfactory inasmuch as the outgased contaminants, presumably both those originally on the wall and those deposited on the wall from the filament flashing, are redeposited on the filament thus recontaminating the latter.

An improved processing method in accordance with the present invention circumvents the recontamination problem. Before flashing the filament in the presence of a forming gas, the bulb wall is first heated to the temperature normally employed for vacuum outgasing. Only after the bulb wall has reached this temperature is flashing of the filament performed. Thereafter, a vacuum is applied to the envelope to remove the outgased contaminants, the bulb wall heating is discontinued, and the bulb walls are allowed to air cool. This entire process is repeated at a series of increasing voltages, for example, but not limited to 6, 9, and 12 volts.

We have found that these improved techniques afford several advantages. The oxides and/or other contaminants normally removed from the filament during flashing are not allowed to migrate to the bulb wall inasmuch as the latter is sufficiently hot to prevent such absorption or adsorption. Those oxides and/or other contaminants which resettle on the filament during the conventional vacuum outgasing of the bulb walls are also not permitted to do so because sufficient hydrogen is present to keep them reduced and in the vapor stage. Therefore, upon evacuation of the envelope the contaminants are removed leaving both the filament and the interior bulb surfaces exceptionally free of contaminants. We have found that applying this technique, a considerable increase in bulb life is achieved over that of comparable commercially available bulbs.

These and other features will be apparent to one skilled in the art upon reading the following detailed description, reference being made to the accompanying drawings in which:

FIG. 1 is an enlarged cross-sectional view of a tungsten halogen light bulb;

FIG. 2 is a schematic of the improved method of processing tungsten halogen light bulbs in accordance with the present invention.

Referring to FIG. 1, there is shown a conventional tungsten halogen light bulb 10 comprising a glass envelope 11 having an interior bulb wall 12 defining a cylindrical cavity 13 in which a transverse coiled tungsten filament 14 is supported on lead wires 16 attached to foil tabs 18 secured in a pinch seal base 20. A pair of terminal wires 22 attached to the lower ends of the tabs 18 are connected to a suitable power source for energizing the filament l4. 7

The envelope 11 is formed of a high melting point glass such as quartz. The envelope has a tipped fill tube 24 on the top surface thereof through which a fill gas and forming gases are introduced or evacuated from the bulb cavity 13 as hereinafter described. The bulb cavity 13 is filled with a suitable halogen containing fill gas. Upon energization of the filament, the bulb operates in a conventional halogen cycle wherein tungsten evaporating from the filament 14 reactsin the vapor phase with halogen in the interior of the bulb to form a volatile tungsten halide. When this tungsten halide diffuses into the high temperature region adjacent the filament 14, it disassociates thereby returning free tungsten to the vicinity of the filament and releasin g the halogen to take place in further regenerative reactions. This cycle is well known and need not be further described. I

During the processing of tungsten halogen light bulbs, it is necessary to remove contaminants from both the filament l4 and the interior bulb wall 12 inasmuch as they have a deleterious affect on the operation of the bulb. Oxides for instance can combine with hydrogen from the fill gas or with hydrogen from the envelope materiai during operation of the bulb and form water vapor. This initiates a water cycle erosion with a filament which greatly shortens the life of the bulb. The oxides and contaminants may also combine with free halogen or tungsten to interfere with a regenerative cycle. The contaminants may also form compounds which deposit on the walls causing blackening and resultant destruction and overheating. We have thus found that thelife of the bulb is directly related to the cleanliness of the bulb cavity prior to introduction of the till gas.

This involves considerationsfor both the cleanliness of the filament l4 and the interior wall 12. The filament 14 in particular may contain residual oxides and contaminants even after extensive cleaning following forming of the coil. The bulb wall on the other hand may contain various adsorbed or absorbed contaminants. The bulb material itself may contain hydroxols which can combine with hydrogen in the fill gas to form water vapor leading to water cycle erosion as described above. We have determined that separate cleaning of the filament and the bulb is insufficient to completely remove the various contaminants. i

Accordingly, an improved process for making tungsten halogen bulbs is shown schematically in FIG. Therein, an untipped bulb 30 includes an unsealed fill tube 32 communicating with the bulb cavity 34. The filament assembly 36 has one lead grounded at 38 and the other lead connected by line 39 in series with a rheostat 40, a switch 42, a power source 44, and a ground 46.

The fill tube 32 is connected by a vacuum coupling 48 to a metered volume 50 of precisely known internal volume. The metered volume 50 is vacuum coupled to a manifold 52 through an on-off valve 54. The manifold 52 includes branch lines, not shown, which are either simultaneously or successively identically vacuum coupled to other valves, metered volumes, and bulbs. The manifold 52 is connected by an on-off valve 56 to a supply of fill gas 58 through a pressure regulator 60. The fill gas 58 comprises a suitable inert gas such as krypton containing a quantity of a halogen compound sufficient to initiate and maintain the desired regenerative cycle in the lamp. In the present invention, a fill gas of krypton with 0.05% methylene bromide is used. The regulator 60 and valve 56 control the resultant pressure in the metered volume 50 and the bulbs 34 just prior to seal-off of the bulbs. Before seal-off, the valve 54 is closed, isolating the bulbs 34 and metered volumes 50 from the manifold 52. There is thus a controlled amount of fill gas 58 available in the metered volume 50 and bulb 34 on each branch line. After further conventional processing is performed to condense the controlled amount of fill gas in each bulb 34, the resultant pressure in the bulb cavity is to 6 atmospheres or thereabout.

The manifold 52 is also connected through an on-off valve 62 to a supply of flushing gas 64 controlled by pressure regulator 66. Argon is used as the flushing gas, although other inert gases could also be used.

The manifold 52 is also connected through an on-off valve 68 to a supply of forming gas 70 controlled by pressure regulator 72. The forming gas preferably comprises a reducing gas such as hydrogen and a carrier gas such as nitrogen.

The manifold 52 is also connected through an on-off valve 74 to a vacuum pump 76 which is controlled by an electrical circuit including a switch 78 and a power source 80.

A heating torch 82 or other suitable heating means is located in proximity to the bulb and is operable to heat the latter to an elevated temperature.

As the unfilled bulb is positioned at the processing station for cleaning, the tungsten as above described may contain various contaminants. To provide a clean bulb filament and cavity, the following process steps are carried out.

Initially valve 74 and valve 54, and any others like it, are actuated to connect the bulb 30 and metered volume 50 to the vacuum pump 76. The switch 78 is then closed to energize the vacuum pump 76 which is operative to evacuate the bulb cavity 34, the metered volume 50, the manifold 52, to a low vacuum of approximately 0.01 torr. The valve 74 is then closed to disconnect the pump from the manifold 52. The valve 68 is then actuated to deliver the forming gas from the supply 70 to the bulb cavity 34. This has the effect of diluting various contained atmospheric gases in the cavity 34. The valve 68 is then closed and valve 74 opened to reconnect the vacuum pump 76 to evacuate the forming gas. If desired, this process may be repeated as necessary to purge all residual gases from the bulb.

The valve 74 is then closed, valve 68 is actuated to fill the bulb with forming gas, and valve 54 is closed to isolate the metered volume 50 and bulb 30 from the manifold 52. The valve 74 is then actuated to evacuate the manifold 52. The bulb is heated by torch or other heating means 82 sufficiently to heat the wall to slightly below its softening point. For a quartz envelope the temperature is about 1500C. This performs an initial outgasing of contaminants absorbed or adsorbed on the wall of the bulb. These contaminants combine partially with the forming gas while a portion thereof are deposited on the filament 36. The valve 54 is then actuated and the vacuum pump 76 evacuates the cavity 34. The cavity may be repeatedly flushed with forming gas as desired to remove the outgased contaminants. In another case this entire outgasing may be deleted and processing begun with the next described step.

The bulb cavity 34 is filled with forming gas, valve 54 closed, and the manifold 52 evacuated. The bulb is heated by torch 82 to slightly below its softening point for a sufficient time to heat the filament 36 to a dull red, about 800C. The rheostat 40 is adjusted to provide a low filament voltage of about 6 volts, and the switch 42 is sequentially opened and closed to repetitively flash the filament 36 while maintaining the heating of the bulb. After the last flash in this initial sequence, valve 54 is opened and the pump 76 evacuates the cavity 34. The torch 82 is then removed and the bulb 30 and filament 36 allowed to cool under vacuum. Thereafter the cavity 34 may be refilled with forming gas and evacuated to purge the forming gas and contaminated mixture from the cavity 34.

The simultaneous heating of the bulb and flashing of the filament prevents cross-redeposition of the contaminants on the interior bulb surfaces and filament components. Thus the heating of the bulb 30 raises the interior wall to a temperature sufficient for outgasing and driving off any remaining absorbed or adsorbed contaminants, while the flashing of the filament 36 serves to drive off any contaminants and oxides, which have resettled or otherwise remain on the filament. These contaminants cannot recombine on the filament 36 because the hydrogen in the forming gas and the temperature together serve to keep them reduced and in the vapor phase. Likewise these contaminants cannot reabsorb or readsorb on the interior bulb surfaces because the wall temperature serves to prevent this.

Thereafter, the bulb cavity is again filled with forming gas, valve 54 closed, and the manifold 52 evacuated. The bulb is then reheated by the torch 82 to just below the softening point for the bulb material and for sufficient time to reheat the filament 36 to about 800C. The rheostat 40 is reset to apply a higher voltage to the filament 36 and the switch 42 is sequentially opened and closed to flash the filament 34. The higher filament temperature resulting from the higher voltage serves to drive off any higher temperature oxides not previously dissociated from the filament. As above, after the desired series of flashes have been performed the bulb cavity 34 is evacuated and the heating means 82 is removed. As many purges as desired may then be made with forming gas to remove the contaminated mixture.

The voltage is progressively increased as desired and the simultaneous heating and flashing is performed until the desired degree of bulb cleanliness has been achieved.

Next, the bulb is purged with the fill gas mixture 58 as many times as necessary to remove any forming gas. The bulb 30 and the metered volume 50 are filled to the desired pressure with the desired halogen and inert gas mixture and valve 54 is closed. Thereafter, further conventional processing is performed to condense the fill gas mixture, including that in the metered volume, in the bulb cavity. The fill tube 32 is tipped off near the bulb 30 and sealed to provide the sealed bulb envelope shown in FIG. 1.

Although only one form of this invention has been shown and described, other forms will be readily apparent to those skilled in the art. Therefore it is not intended to limit the scope of this invention by the embodiment selected for the purpose of this disclosure, but only by the claims which follow.

We claim:

1. A method of processing tungsten halogen light bulbs wherein said bulb includes a glass envelope having a contaminated interior bulb wall defining an open ended cavity in which a contaminated tungsten filament is supported, comprising the steps of:

l. filling the cavity with a reducing gas,

2. heating the envelope to a temperature sufficient to outgas the contaminants on said bulb wall,

3. energizing the filament when the bulb wall has reached said temperature to expel the contaminants from the filament, continuing heating of the bulb wall to maintain a temperature during said energizing sufficient to prevent absorption or adsorption of the expelled contaminants thereon,

4. removing the contaminated gas,

5. refilling said cavity with a halogen containing gas,

and

6. sealing said open ended cavity to retain said halogen containing gas therein.

2. A method of processing tungsten halogen light bulbs wherein the bulb includes a glass envelope having an interior bulb wall containing absorbed and adsorbed contaminants, said wall defining a cavity with an open end in which a tungsten filament having contaminants thereon including oxides is supported, comprising the steps of:

l. filling said cavity with a gas mixture including a reducing gas,

2. heating said envelope to a temperature sufficient to outgas the contaminants on said bulb wall to said gas mixture with a portion thereof depositing on the filament,

3. flashing said filament when said bulb wall has reached said temperature, said flashing being sufficient to expel the contaminants from the filament 5 to the mixture whereat the oxides are reduced by the reducing gas, said temperature of the bulb wall being continuously maintained during all filament flashing to prevent resettling of the expelled contaminants thereon,

l0 4. removing the contaminated gas mixture from the cavity,

5. refilling said cavity with a gaseous mixture containing sufficient halogen to maintain a regenerative halogen cycle,

6. and sealing the open end of said cavity to retain said gaseous mixture therein.

3. A method of processing tungsten halogen light bulbs wherein said bulb includes a glass envelope having an interior wall with adsorbed or absorbed contaminants thereon, said wall defining a cylindrical cavity in which a tungsten filament is supported, said filament having contaminants including oxides thereon, comprising the steps of:

1. filling said cavity with a reducing forming gas,

2. heating the bulb wall to slightly below the melting point of glass to a temperature at which the contaminants on said wall are driven therefrom for reduction by said forming gas,

3. applying a voltage to said filament, while continually heating said bulb throughout application of voltage to said filament so as to drive the oxides and contaminants from said filament to said forming gas for reduction thereby,

4. evacuating the cavity to remove the contaminated forming gas mixture and cooling said envelope,

5. sequential repetition of steps 1 through 4 inclusive,

with increasing filament voltages until a predetermined removal of contaminants has been achieved with the continual heating of said bulb being present during each application of increased filament voltage, I

6. filling said cavity with a halogen containing gaseous mixture sufficient to initiate and maintain an operative regenerative cycle in said cavity, and

7. sealing said cavity to retain said gaseous mixture therein. 

1. FILLING THE CAVITY WITH A REDUCING GAS,
 1. A METHOD OF PROCESSING TUNGSTEN HALOGEN LIGHT BULBS WHEREIN SAID BULB INCLUDES A GLASS ENVELOPE HAVING A CONTAMINATED INTERIOR BULB WALL DEFINING AN OPEN ENDED CAVITY IN WHICH A CONTAMINATED TUNGSTEN FILAMENT IS SUPPORTED, COMPRISING THE STEPS OF:
 2. HEATING THE ENVELOPE TO A TEMPERATURE SUFFICIENT TO OUTGAS THE CONTAMINANTS ON SAID BULB WALL,
 2. heating the bulb wall to slightly below the melting point of glass to a temperature at which the contaminants on said wall are driven therefrom for reduction by said forming gas,
 2. heating said envelope to a temperature sufficient to outgas the contaminants on said bulb wall to said gas mixture with a portion thereof depositing on the filament,
 2. A method of processing tungsten halogen light bulbs wherein the bulb includes a glass envelope having an interior bulb wall containing absorbed and adsorbed contaminants, said wall defining a cavity with an open end in which a tungsten filament having contaminants thereon including oxides is supported, comprising the steps of:
 2. heating the envelope to a temperature sufficient to outgas the contaminants on said bulb wall,
 3. energizing the filament when the bulb wall has reached said temperature to expel the contaminants from the filament, continuing heating of the bulb wall to maintain a temperature during said energizing sufficient to prevent absorption or adsorption of the expelled contaminants thereon,
 3. flashing said filament when said bulb wall has reached said temperature, said flashing being sufficient to expel the contaminants from the filament to the mixture whereat the oxides are reduced by the reducing gas, said temperature of the bulb wall being continuously maintained during all filament flashing to prevent resettling of the expelled contaminants thereon,
 3. A method of processing tungsten halogen light bulbs wherein said bulb includes a glass envelope having an interior wall with adsorbed or absorbed contaminants thereon, said wall defining a cylindrical cavity in which a tungsten filament is supported, said filament having contaminants including oxides thereon, comprising the steps of:
 3. applying a voltage to said filament, while continually heating said bulb throughout application of voltage to said filament so as to drive the oxides and contaminants from said filament to said forming gas for reduction thereby,
 3. ENERGIZING THE FILAMENT WHEN THE BULB WALL HAS REACHED SAID TEMPERATURE TO EXPELL THE CONTAMINANTS FROM THE FILAMENT, CONTINUING HEATING OF THE BULB WALL TO MAINTAIN A TEMPERATURE DURING SAID ENERGIZING SUFFICIENT TO PREVENT ABSORPTION OR ADSORPTION OF THE EXPELLED CONTAMINANTS THEREON,
 4. REMOVING THE CONTAMINATED GAS,
 4. evacuating the cavity to remove the contaminated forming gas mixture and cooling said envelope,
 4. removing the contaminated gas mixture from the cavity,
 4. removing the contaminated gas,
 5. refilling said cavity with a halogen containing gas, and
 5. refilling said cavity with a gaseous mixture containing sufficient halogen to maintain a regenerative halogen cycle,
 5. sequential repetition of steps 1 through 4 inclusive, with increasing filament voltages until a predetermined removal of contaminants has been achieved with the continual heating of said bulb being present during each application of increased filament voltage,
 5. REFILLING SAID CAVITY WITH A HALOGEN CONTAINING GAS, AND
 6. filling said cavity with a halogen containing gaseous mixture sufficient to initiate and maintain an operative regenerative cycle in said cavity, and
 6. and sealing the open end of said cavity to retain said gaseous mixture therein.
 6. sealing said open ended cavity to retain said halogen containing gas therein.
 6. SEALING SAID OPEN ENDED CAVITY TO RETAIN SAID HALOGEN CONTAINING GAS THEREIN.
 7. sealing said cavity to retain said gaseous mixture therein. 